Use of strontium isotope ratios in potential geolocation of Ajnala skeletal remains: a forensic archeological study.

Stable isotope methods for provenance of unidentified human remains are relatively a newer field of enquiry in forensic archeology. It is of great interest for forensic experts these days. The application of strontium isotope analyses for estimating geolocation of archeological remains is of great interest in bioarcheology and modern forensics. The strontium (Sr) isotope composition of human bones and teeth has been widely used to reconstruct an individual's geo-affiliation, residential mobility, and migration history. Thousands of unknown human remains, reportedly belonging to 282 Indian soldiers of 26th Native Bengal regiment and killed in 1857, were exhumed non-scientifically from an abandoned well situated underneath a religious structure at Ajnala (Amritsar, India). Whether these remains belonged to the individuals, local or non-local to the site, was the important forensic archeological question to be answered by doing their thorough forensic anthropological examinations. In the present study, 27 mandibular teeth (18 s molars, 6 first molars, and 3 premolars) collected from the Ajnala skeletal assemblage were processed for strontium isotope analysis, and the measured ratios were compared with published isotope baseline data to estimate the locality status of these remains. The Sr isotopic values were concentrated in the range of 0.7175 to 0.7270. The comparative analysis of isotopic ratios revealed that most individuals buried in the Ajnala well have 87Sr/86Sr values close to the river as well as groundwater of the Gangetic plain (less radiogenic 87Sr/86Sr ~ 0.716); most likely originated near Varanasi (Uttar Pradesh, India) region, whereas the individuals with higher 87Sr/86Sr ratios (~ 0.7200) probably resided in the West Bengal and Bihar areas where the river as well as groundwater of the Gangetic plain is relatively more radiogenic. Thus, the strontium isotope results reveal that the Ajnala individuals did not grow up or live in the Amritsar region during their childhood, and this observation complemented the previous forensic anthropological and molecular findings. There is very little Indian data on the bioavailable strontium, so the inferences from the present study estimating Sr isotope abundances are expected to provide baseline data for future forensic provenance studies that will contribute to the global efforts of mapping Sr isotope variations by the isotope community.

Strontium isotope evidence for landscape use by early hominins.

Ranging and residence patterns among early hominins have been indirectly inferred from morphology, stone-tool sourcing, referential models and phylogenetic models. However, the highly uncertain nature of such reconstructions limits our understanding of early hominin ecology, biology, social structure and evolution. We investigated landscape use in Australopithecus africanus and Paranthropus robustus from the Sterkfontein and Swartkrans cave sites in South Africa using strontium isotope analysis, a method that can help to identify the geological substrate on which an animal lived during tooth mineralization. Here we show that a higher proportion of small hominins than large hominins had non-local strontium isotope compositions. Given the relatively high levels of sexual dimorphism in early hominins, the smaller teeth are likely to represent female individuals, thus indicating that females were more likely than males to disperse from their natal groups. This is similar to the dispersal pattern found in chimpanzees, bonobos and many human groups, but dissimilar from that of most gorillas and other primates. The small proportion of demonstrably non-local large hominin individuals could indicate that male australopiths had relatively small home ranges, or that they preferred dolomitic landscapes.

A comparison of pretreatment methods for the analysis of phosphate oxygen isotope ratios in bioapatite.

RATIONALE: The integrity of the biological phosphate oxygen isotope (δ(18)O(p) ) signal is thought to be contingent upon the complete removal of competing sources of oxygen such as associated organic matter. A range of pretreatment methods to purify phosphate material from competing sources of oxygen has been reported, with contradictory evidence on the usefulness and efficiency of one or another. Yet, a systematic comparison of these techniques for bioapatite phosphate has not been conducted. METHODS: Chemical and thermal pretreatment techniques were tested for their effectiveness at removing organic matter and the likelihood that they modify original δ(18)O values. The test was performed in inorganic (synthetic apatite and a phosphorite rock) and organic (bone and tooth tissues) phosphate materials for which we had an expectation of the actual original δ(18)O(p) value. Analysis of nitrogen content (wt.%), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were employed. RESULTS: We detected variable efficiency at removing organic matter between pretreatment methods with no correlation to any specific structural change. The δ(18)O(p) results showed considerable variation between samples pretreated with the different methods and the untreated samples, with a compositional range of up to 4.5 ‰ in the bone samples. Variations of the δ(18)O(p) values within error were found for tooth enamel, phosphorite rock and inorganic apatite. CONCLUSIONS: We recommend a cautious approach when interpreting and comparing δ(18)O(p) data from bone samples treated with different pretreatment protocols. In general, the untreated samples seem to show δ(18)O(p) values closer to the expected ones. According to our results, pretreatment is completely unnecessary in highly mineralized tissues.

Comparison between strip sampling and laser ablation methods to infer seasonal movements from intra-tooth strontium isotopes profiles in migratory caribou.

Strontium isotopes analysis is a powerful tool in the study of past animal movements, notably the sequential analysis of tooth enamel to reconstruct individual movements in a time-series. Compared to traditional solution analysis, high resolution sampling using laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) has the potential to reflect fine scale mobility. However, the averaging of the 87Sr/86Sr intake during the enamel mineralization process may limit fine scale inferences. We compared solution and LA-MC-ICP-MS 87Sr/86Sr intra-tooth profiles from the second and third molars of 5 caribou from the Western Arctic herd, Alaska. Profiles from both methods showed similar trends, reflecting the seasonal migratory movements, but LA-MC-ICP-MS profiles showed a less damped 87Sr/86Sr signal than solution profiles. Geographic assignments of the profile endmembers to the known summer and winter ranges were consistent between methods and with the expected timing of enamel formation but showed discrepancy at a finer scale. Variations on LA-MC-ICP-MS profiles, consistent with expected seasonal movements, suggested more than an admixture of the endmember values. However, more work in understanding enamel formation in Rangifer, and other ungulates, and how 87Sr/86Sr daily intake translates into enamel are needed to assess the real resolution that can be achieved with LA-MC-ICP-MS.

The genetic prehistory of the New World Arctic.

The New World Arctic, the last region of the Americas to be populated by humans, has a relatively well-researched archaeology, but an understanding of its genetic history is lacking. We present genome-wide sequence data from ancient and present-day humans from Greenland, Arctic Canada, Alaska, Aleutian Islands, and Siberia. We show that Paleo-Eskimos (~3000 BCE to 1300 CE) represent a migration pulse into the Americas independent of both Native American and Inuit expansions. Furthermore, the genetic continuity characterizing the Paleo-Eskimo period was interrupted by the arrival of a new population, representing the ancestors of present-day Inuit, with evidence of past gene flow between these lineages. Despite periodic abandonment of major Arctic regions, a single Paleo-Eskimo metapopulation likely survived in near-isolation for more than 4000 years, only to vanish around 700 years ago.

Strontium isotope ratios (87Sr/86Sr) of tooth enamel: a comparison of solution and laser ablation multicollector inductively coupled plasma mass spectrometry methods.

Strontium isotope ratios (87Sr/86Sr) in tooth enamel provide a means to investigate migration and landscape use in humans and other animals. Established methods for measuring (87)Sr/(86)Sr in teeth use bulk sampling (5-20 mg) and labor-intensive elemental purification procedures before analysis by either thermal ionization mass spectrometry (TIMS) or multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Another method for measuring 87Sr/86Sr is laser ablation MC-ICP-MS, but concerns have been expressed about its accuracy for measuring tooth enamel. In this study we test the precision and accuracy of the technique by analyzing 30 modern rodent teeth from the Sterkfontein Valley, South Africa by laser ablation MC-ICP-MS and solution MC-ICP-MS. The results show a mean difference in 87Sr/86Sr measured by laser ablation and by solution of 0.0003 +/- 0.0002. This degree of precision is well within the margin necessary for investigating the potential geographic origins of humans or animals in many areas of the world. Because laser ablation is faster, less expensive, and less destructive than bulk sampling solution methods, it opens the possibility for conducting 87Sr/86Sr analyses of intra-tooth samples and small and/or rare specimens such as micromammal and fossil teeth.